This is caused by either corrupt firmware or you installed an app which caused a corruption in the load. Did this start immediately following installing an app?
The simplest potential way to resolve is re install the firmware. Go to Archos.com, choose Downloads and firmware which matches your version of 7 and apply as the instructions. This will normally resolve without losing any apps.
If applying the Firmware does not resolve, you will have to do a wipe and reinstall of firmware. This is similar to first option but you lose all stored apps and data. This is accomplished by booting the A7 by pushing the Up volume and the Power button as you boot up. The recovery menu will appear. You will need to choose recover system.
Read the instructions Archos has for this as well. My instructions are brief, It is not hard. it does require you to have the Firmware available on your PC and ready to copy over to the device as instructed.

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